Ultrasonic catheters have been proposed. An example of such a catheter is shown in U.S. Pat. No. 7,540,852, the disclosure of which is fully incorporated herein by reference. While this catheter achieves the desired result of providing enhanced disruption of blood vessel obstructions, the present disclosure proposes certain modifications or improvements to enhance the results achieved during an endovascular procedure in terms of clearing an obstruction from a vessel (such as, for example, an atherectomy for removing atherosclerosis from a blood vessel, or for crossing an occlusion).